The present invention relates to a steering angle detecting apparatus for a vehicle detecting an absolute steering angle of a steering mechanism and an electric power steering apparatus including the steering angle detecting apparatus.
In recent years, as a steering device for vehicles, such as cars and trucks, an electric power steering apparatus has been widely spread which drives an electric motor on the basis of the steering torque of a steering wheel by the driver and applies steering assist force to a steering mechanism to reduce the steering effort to be applied by the driver.
In this type of electric power steering apparatus, many control functions using the steering angle of the steering wheel have been developed in order to ensure the handling stability and comfort of the vehicle. It is necessary to detect the steering angle as soon as possible in order to rapidly fulfill the control function on the basis of the steering angle after the vehicle is started.
There is proposed an electric power steering apparatus including plural sensors so as to detect detects the steering angle rapidly (for example, see PTL 1). In order to accurately detect the absolute rotational position of a steering wheel, this technique includes a first resolver detecting a first steering angle, which is the rotation angle of a steering shaft connected to a steering wheel, a second resolver having pole pairs different in number from those of the first resolver so as to detect a second steering angle, which is the rotation angle of the steering shaft, and a third resolver detecting the rotation angle (motor electric angle) of a motor which assists steering, and calculates the absolute rotation angular position of the steering wheel from the first steering angle, the second steering angle, and the motor electric angle.
In addition, there is proposed a steering angle detecting apparatus detecting the absolute steering angle of a steering wheel on the basis of its own neutral position, storing, in a memory, the absolute steering angle at the moment when an ignition switch is turned off, and detecting the absolute steering angle on the basis of the stored value when the ignition switch is turned on (for example, see PTL 2).